if isBlue == true {
            blueView.backgroundColor = greenView.backgroundColor
        } else {
            blueView.backgroundColor = UIColor(red: 0/255.0, green: 128/255.0, blue: 255/255.0, alpha: 1)
        }
        isBlue = !isBlue
    }
    @IBAction func didBeginPanGesture(_ sender: UIPanGestureRecognizer) {
        var point = sender.location(in: view)
        blueView.center = CGPoint(x: point.x, y: point.y)
    }